Export (0) Print
Expand All
Expand Minimize

Compiler Error CS1640 

Error Message

foreach statement cannot operate on variables of type 'type' because it implements multiple instantiations of 'interface', try casting to a specific interface instantiation

The type inherits from two or more instances of IEnumerator<T>, which means there is not a unique enumeration of the type that foreach could use. Specify the type of IEnumerator<T> or use another looping construct.

Example

The following sample generates CS1640:

// CS1640.cs

using System;
using System.Collections;
using System.Collections.Generic;

public class C : IEnumerable, IEnumerable<int>, IEnumerable<string>
{
    IEnumerator<int> IEnumerable<int>.GetEnumerator()
    {
        yield break;
    }

    IEnumerator<string> IEnumerable<string>.GetEnumerator()
    {
        yield break;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return (IEnumerator)((IEnumerable<string>)this).GetEnumerator();
    }
}

public class Test
{
    public static int Main()
    {
        foreach (int i in new C()){}    // CS1640

        // Try specifing the type of IEnumerable<T>
        // foreach (int i in (IEnumerable<int>)new C()){}
        return 1;
    }
}

Community Additions

ADD
Show:
© 2015 Microsoft